Field of the Invention
The present invention relates to an actuator control apparatus.
Description of the Related Art
In image pickup devices such as a digital still camera and a digital video camera, various mechanisms are controlled with feedforward control or feedback control. For example, in positional control of diaphragm blades for performing AE (Automatic Exposure) control, performing the feedback control has such an advantage that convergence time becomes shorter than that when the feedforward control is performed.
For example, FIG. 14 of Japanese Patent Application Laid-Open Publication No. 2009-63702 discloses an image pickup device that adjusts a light amount of inputted light by controlling an aperture area of an iris (lens diaphragm) using a servo mechanism. In such an image pickup device, a current position of the iris is detected using a hall sensor as a position sensor, and feedback control to adjust the duty cycle of a PWM (Pulse Width Modulation) signal for driving a motor is performed so that a hall value corresponding to the current position converges on that corresponding to a target position.
As such, a diaphragm position is detected using an output of a position sensor such as a hall sensor, thereby being able to perform positional control of a diaphragm mechanism (diaphragm blades) with the feedback control.
In the image pickup device in FIG. 14 of Japanese Patent Application Laid-Open Publication No. 2009-63702, the output signal of the hall sensor is converted into a digital signal by ADC (Analog-Digital Converter) and is subjected to digital signal processing.
However, in such feedback control that the positional control of a control target is made in accordance with a result of the digital signal processing, if the sampling frequency of ADC and/or the operation frequency of the digital signal processing circuit becomes a frequency equal to or smaller than twice the audible range (approximately equal to or smaller than 40 kHz), a driving noise of an actuator becomes audible. Thus, if such digital feedback control is applied to an image pickup device, the driving noise is recorded as sound while shooting video.
Whereas, if the ADC sampling frequency is further increased, speeding-up in the ADC itself and/or the digital signal processing circuit results in increase in circuit scale and/or power consumption.